Commercially available moisture probes typically are one-use devices that result in significant waste and expense or are reusable but must be re-calibrated or checked for accuracy before new use. Re-calibrating a reusable probe before use requires significant time. In addition, reusable probes may become inaccurate due to aging, but typically users do not have the equipment and capability to check the accuracy of their probes. Therefore, reusable probes are often used for many months or even years without being tested for accuracy. Use of inaccurate probes can lead the user to make inappropriate decisions and significant problems based on incorrect data: for example, if a moisture probe indicates that a concrete floor is dry enough to receive a floor covering or coating, but the floor is in reality too wet, then a floor covering or coating will be installed which later will fail due to the unrecognized high moisture condition. Use of inaccurate probes can, thus, have a significant economic impact on a commercial facility when floor coverings or coatings must be repaired or replaced after the facility has been put into operation.
In addition, commercially available relative humidity probes are expensive because they comprise a sensing element and electronics package all in the probe head that is inserted into the concrete. In addition, cost is a very relevant factor in the adoption of moisture probe technology. Typical prices of moisture probes commercially available in the United States range from $50 to over $250, and the cost of associated handheld meters ranges from several hundred dollars to nearly $700. Compared to anhydrous calcium chloride test kits (ASTM F1869) which cost approximately $8.00 per test, the high price of moisture probes has been a barrier to wide-spread acceptance in the floor coverings and coatings industry for preinstallation testing.
Further, commercially available probe systems often employ an outer housing and an inner housing, the outer housing used to line the drilled hole in concrete to isolate the sidewall of the hole from the sensor which is positioned inside the inner housing. Prior art systems utilize fins along the sidewall of the outer housing to define a volume. This volume represents a “dead volume” that serves as the volume the sensor tests. In prior art systems the volume is defined by a portion of the sidewall of the hole, the space between the outer housing and the inner housing and the space between the inner housing and the sensor plus any additional volume within the sensor housing. Thus, because the probe itself takes up a significant volume within the sleeve, a typical commercially available probe has a large volume (for example some systems have a volume around 2650 mm3) which must equilibrate with the concrete.
Probes using existing technology require longer than desirable times to equilibrate, an issue which is magnified for reusable probes that require calibration checking before use. For example, users currently place probes in concrete and have to return to the jobsite three days later to obtain readings, in accordance with ASTM F2170-02, “Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes.”